Adjustable coupling system



March 2, 1943. F, CURTIS ADJUSTABLE COUPLING SYSTEM Filed Aug. 23, 1941 B W- E mun D I w m MA 6 U M Y w m E O- B A 0 m E 5; WWR 00 W WM O- R E E E M T m M T I A m MM "F N l B m MU m FIG. I.

m ijw wmLmx I s 5: 3 28.5 8

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ATTORNEY Patented Mar. 2, 1943 ADJUSTABLE COUPLING SYSTEM Leslie F. Curtis, Great Neck, N.' Y., assignor to Hazeltine Corporation, a corporation of Delaware Application August 23, 1941, Serial No. 408,032

12 Claims.

This invention relates to adjustable coupling systems and more particularly to such systems of a type in which it is desired to adjust a very small inductive coupling between two inductors orin which it is desired to adjust the inductive coupling between two inductors to zero.

It is sometimes desirable in electrical systems to adjust a very small inductive coupling between two inductors. Band-pass selectors used, for example, in radio receivers generally comprise two inductors which are loosely inductively coupled and it is frequently desirable to adjust the magnitude of such coupling thereby to adjust the band width of the selector. Also, an electrical circuit may comprise two rather closely-spaced inductors between which it is desired that there be no inductive coupling. Various arrangements have been proposed by which such inductors may be so spaced that no coupling exists between them. One such arrangement is disclosed inLetters Patent No. 1,577,421, granted March 16, 1926, to Louis A. Hazeltine. However, in constructing an arrangement ofthe type under consideration, it is frequently found to be diflicult so to position the inductors that no inductive coupling exexcited. It is accordingly desirable to provide a means for adjusting, with either polarity, a very small coupling between such inductors, thereby to reduce the total efiective coupling between such inductors to zero.

It is an object of the present invention to provide an improved adjustable coupling system for adjusting a very small inductive coupling between two inductors.

It is another object of the present invention to provide an adjustable coupling system for adjusting to zero the residual inductive coupling between two inductors so disposed that only an inductive coupling of very small value exists between the inductors.

In accordance with the invention, an adjustable coupling system comprises a first inductor,

an input circuit connected to the first inductor, and a second inductor so disposed in the magnetic field of the first inductor that the second inductor is substantially inductively uncoupled with the first shoulder. The system also com- 'ists therebetween when one of the inductors is prises an output circuit connected to the second inductor and a movable conductive inductivecoupling means substantially nonselective over v the frequency range of the system so disposed with reference to the inductors that, in a given position in its path of motion, it is substantially uncoupled with at least one of the inductors and,

in another given position in its path of motion, it is substantially coupled with both of the inductors. Means are provided for moving the above-mentioned coupling means in the said path of motion to adjust the coupling between the inductors.

In accordance with a preferred embodiment of the invention, the conductive inductive-coupling means is so disposed that, in positions in its path of motion on opposite sides of the above-mentioned given position, it substantially couple the inductors with a polarity dependent upon the direction in the path from such given position. Also in this preferred embodiment of the invention, the means for moving the adjustable coupling means comprises means for movingthe coupling means through the above-mentioned given position to adjust, with either polarity, the coupling between th inductors.

For a better understanding of the invention, together with other and further advantages thereof, reference is had to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Fig. 1 of the drawing is a circuit diagram, partly schematic, of a complete superheterodyne receiver including an adjustable coupling system in accordance with the invention in the intermediate-frequency channel thereof for the purpose of adjusting the selectivity of the receiver; Figs. 2, 4 and 5 illustrate modifications of the portion of the system of Fig. 1 constituting the present invention; while Fig. 3 comprises graphs utilized to explain the operation of the portion of the circuit of Fig. 1 comprising the present invention.

Referring now more particularly to Fig. 1 of the drawing, there is shown a circuit diagram, partially schematic, of a complete modulated-carrier signal receiver of the superheterodyne type embodying the invention. The receiver comprises, in cascade, an antenna-ground circuit l0, II, a radio-frequency amplifier l2 of one or more stages, a frequency-changer or oscillator-modulator l3, intermediate-frequency amplifiers l4 and I5, each of one or more stages, coupled by means of a coupling system H, a detector and automatic amplification control or A. V. C. supply IB, an audio-frequency amplifier IQ of one or more stages, and a sound reproducer 20. Au-

tomatic amplification control is secured in a wellbodying the present invention, the circuit described constitutes, in general, a conventional superheterodyne receiver including automatic volume control. The operation of such a receiver being well understood in the art, a detailed description thereof is deemed unnecessary herein. In brief, however, signals intercepted by antennaground circuit H], H are selected and amplified in radio-frequency amplifier l2 and translated to oscillator-modulator I3, wherein they are converted to an intermediate-frequency signal. The intermediate-frequency signal is selectively amplified in intermediate-frequency amplifier l4 and translated through the coupling system I! of the invention, to be described in detail hereinafter, and second intermediate-frequency amplifier |5 to detector I6, wherein the audiofrequency signals and the A. V. C. biasing poten tials are derived. The audio-frequency signals are, in turn, amplified in audio-frequency amplifier l9 and supplied to sound reproducer 20 for reproduction. The automatic amplification control bias derived from unit I6 is effective to control the amplification of one or more of the units 2, I3, I 4 and I5 to maintain the signal input to detector l6 within a relatively narrow range for a wide range of received signal intensities.

Referring now more particularly to the portion of the circuit comprising the present invention, an adjustable coupling system I! is provided for coupling the output circuit of first intermediatefrequency amplifier M to the input circuit of second intermediate-frequency amplifier l5. This adjustable coupling system is preferably enclosed in a conductive shield l8 and comprises a first inductor 2| included in an input circuit connected to the output circuit of intermediatefrequency amplifier l4 and a second inductor 22 so disposed in the magnetic field of the first inductor 2| that the second inductor 22 is substantially inductively uncoupled with the first inductor 2| as with their axes normal to each other, as illustrated. Expressed somewhat differently, the second inductor is disposed in the magnetic field of the first inductor so that the axes of the inductors are in a common plane and have such an angle with respect to the line of centers of the inductors that the second inductor is substantially inductively uncoupled with the first inductor. The inductor 22 is included in the output circuit of the coupling system and is coupled directly to the input circuit of second intermediate-frequency amplifier IS.

A movable conductive inductive coupling means is so disposed with reference to inductors 2| and 22 that, in a given position in its path of motion, it is substantially uncoupled with at least one of the inductors 2|, 22 and substantially coupled to the other of said inductors and, in another given position in its path of motion, it is substantially coupled with both of the inductors 2|, 22. This movable inductive-coupling means comprises a disc 23 of highly-conductive material and is substantially nonselective over the frequency range of the system and is adapted to be rotated about an axis 24 normal to the plane including the axes of inductors 2|, 22, the last-named axes being normal to each other. The axis of the movable inductive-coupling means 23 is preferably in the line of centers of the inductors 2| 22. In order to move'the disc 23about the axis 24, there is provided an arm 25 of insulating material to which the disc 23' is rigidly fixed, the arm. 25 being mounted to rotate about the axis 24. The means for moving the disc 23 in its path of motion to adjust the coupling between the inductors 2|, 22 also includes a thumb screw 26, threaded in a stationary member 21' and adapted to bear against one end of arm 25, as well as a biasing means, such as a spring 28, connected between the other end of arm 25 and a stationary pin 29.

The movable inductive-coupling means 23, therefore, is so disposed with reference to the inductors 2|, 22 that in a given position in its path of motion it is substantially uncoupled with at least one of the inductors 2|, 22, and in other positions in its path of motionon opposite sides of the given position it substantially couples the inductors with a polarity dependent upon .the

direction of' its position in its path of motion from the given position. The thumb screw 26, the cooperating stationary member 21, and the biasing spring 28 are included in a means for moving the coupling means 23 in its path and through the given position to adjust to either polarity the coupling between the inductors Likewise, it may be stated that the movable inductive-coupling means 23 is so disposed with reference to the inductors 2|, 22 that in 'a first given position in its path of motion it is substantially uncoupled with one of the inductors and substantially coupled with the other of the inductors, in a second given position in its path of motion it is'substantially uncoupled with the other of the inductors and substantially coupled with one of the inductors, and in other positions in its path of motion on opposite sides of one of the given positions it substantially couples the inductors with a polarity dependent upon the "direction in the path from one 'ofthe given positions. The thumb screw- 26 is included in a means for moving the coupling means 23 in its path through one of the given positions to adjust to either polaritythe coupling between the inductors 2|, 22.

Expressed in a somewhat difierent manner, the movable inductive-coupling means 23 is so disposed with reference to the inductors 2|, 22 that in a first given position in its path of motion it is substantially uncoupled with one of the inductors and substantially coupled with the other of the inductors, in a second given position in its path of motion it is substantially uncoupled with the other of the inductors and substantially coupled with the said one of the inductors, and in other positions in its path of motion including positions between the given positions it is substantially coupled with both of the inductors.

In considering the operation of the arrangement of Fig. 1, it will be seen that, in the absence of disc 23, there is substantially no coupling between the inductor 2| and the inductor 22. The reason that inductor 22 is uncoupled to inductor 2| is that the turns of inductor 22 are substantially parallel to the lines of force in the field of inductor 2|. Furthermore, it will be seen that, in the presence of the coupling adjusting means 23 between inductors 2| and 22, for any position of disc 23 other than that parallel to or including the axis of one of the inductors, the disc is loosely coupled to both the inductors 2| and 22 and hence serves indirectly to couple them to each other. Further, adjustment of the screw 26 is effective to vary the position of disc 23 thereby to vary the amount of such Each 01' the sides of the shield acts like a stacoupling between inductors 2| and 22.

It will be understood that inductors 2| and 22 may comprise the inductors of a double-tuned band-pass selector so that adjustment of the coupling between these inductors is effective to vary the selectivity of the receiver in a manner well understood in the art. In such aband-pass selector, it is, of course, only desirable to adjust the coupling between two rather low values of the same polarity. However, it will be understood that the inductors 2| and 22 can be connected in parallel with the coupled main inductors of a conventional double-tuned band-pass selector and that the band width of such a selector can be adjusted by varying both the magnitude and polarity of the coupling between inductors 2| and 22 to aid or oppose the coupling between the main inductors.

In order to explain the operation-of the adjustable coupling system of the invention under these conditions, it will be assumed the angle 02 designates the angle between the axis of disc 23 and the axis of inductor 2|, as indicated. It will be seen that, in a given position in the path of motion of disc 23, namely, when 02 is 90, the disc 23 is substantially uncoupled with inductor 2| and has maximum coupling to'inductor 22. It will also be seen that, in a second given position, namely, when 02 is zero degrees, the disc 23 is substantially uncoupled to inductor 22 and has the maximum coupling with inductor 2|. Adjustment of the disc 23 through either of these given positions is effective to adjust the coupling between inductors 2| and 22 so that the polarity of coupling is dependent upon the direction in the path of motion of disc 23 from the given position selected in which the coupling is zero.

The following equations are approximately valid for the coupling system of Fig. 1:

k21-23=K21-23 cos 02 (l) 7C23 22=K23 22 sin 62 (2) 21-22= 2i23 2322 Sill 2 003 2 I where tionary reflecting surface. The upper and lower surfaces oi the shield are spaced the same distance from the axis of inductor 2| and the center of inductor 22. Thus, the coupling effect of the bottom of shield l3 between coils 2| and 22 is effectively neutralized by the coupling effect of the top of shield l8 inasmuch as these surfaces are symmetrical with respect to the inductors 2| and 22. Inasmuch as each end of the shield is no more closely coupled to the inductor remote therefrom than the inductor adjacent thereto is coupled to the remote inductor, circulating currents in the ends of the shield have very little efl'ect on the coupling between the inductors. It is also important that the material of which the shield be made should be of a material having a low specific resistance, such as copper or aluminum, if the coupling between inductors 2| and 22 is to be reduced to zero by an arrangement in accordance with the invention. Metals such as iron introduce a complex coupling such as a coupling equivalent to mutual resistance and inductance. Disc 23 may then be made to balance out the reactive components but it will not be effective to balance out the resistive component.

Other positions of inductors 2| and 22, with the axes oi! the inductors coplanar, also provide zero coupling therebetween in the absence of disc 23 and may, therefore, be used in arrangements in accordance with the present invention.

Reference is made to Fig. 2 for an explanation of why this is true. Elements of Fig. 2 which correspond to those of Fig. 1 have identical reference numerals. The following equation is kz1-2a=the coeihcient of coupling between inductor 2| and disc 23;

k2a 22: the coefficient of coupling between disc 23 and inductor 22;

7c'z122=the coefficient of coupling between inductor 2 and inductor 22;

Kzi z3=the maximum coeflicient of coupling between inductor 2| and disc 23; and

K23 22=the maximum coefllcient of coupling between disc 23 and inductor 22.

From Equation 3 it is seen that for negative values 02 or for values of 02 greater than190" the polarity of coupling or the sign of the coeflicient of coupling reverses. The equations are based on the assumption that the separation of the inductors is large relative to the dimensions of the inductors. However, arrangements in accordance with the invention have been constructed in which the separation of the inductors was quite small and have been found to be practicable.

Inasmuch as very small values of coefiicient of coupling are being dealt with in the arrangement of Fig. 1, it is advisable to observe certain precautions in designing the shield l8 therefor as otherwise circulating currents in the shield modify the field between inductors 2| and 22.

approximately valid for the arrangement of Fig. 2 under the condition of zero coupling between inductors 2| and 22 and in the absence of any coupling effect of disc 23 between inductors 2| and 22:

1 cos 0 sin 0 C032 1 +3 cos 6 1 +3 cos 0 where i 01 and 03 represent the angles between the axes of inductors 2| and 22, respectively, and their line of centers.

The following equations represent the conditions for which the coupling between disc 23 and inductors 2| and 22, respectively, is zero:

zero coupling between inductors 2| and 22 in the absence of disc 23.

Cos 6 Degrees Degree;

l Ifsed in arrangement of Fig. 1

The disc 23 may be considered as a shortcircuited winding and the coefficient of coupling for any of the arrangements just described may be calculated for any value of 02 from the equation:

k21-22=K2 123K2322 sin (0201) sin (02-03) ('7) where 01 and 03 are determined from the table given above.

Thus, if 01 equals 30 degres'and equals 74.5

degrees, the disc 23 has no coupling to inductor 22 when 02 equals 30 degrees and has no coupling to inductor 2| when 02 equals 74.5 degrees. The maximum coupling from the disc to inductor 2| and inductor 22, respectively, occurs when disc 23 is displaced 90 degrees from these positions. For any angle of 02 the over-all coefiicient of coupling under these conditions is:

- rangement of Fig. 4 inductor 2| has an axis perpendicular to the plane of the paper, inductor 22 has an axis in the plane of t, e paper normal to the'line of centers, while disc 23 has an axis of rotation in the plane of the paper and perpendicular to the axes of inductors..21}and 22. It will be understood that, as used in th' specification, the term disc" is intended {t include either a circular disc, as in the arrangement of Fig. 1, or an annular disc, as in the arrangement of Fig. 4. The operation of the system ofl ig. 4 is in all respects similar to that of Fig. 1 and the equations representing the several coeificients of coupling can be derived in an analogous manner.

Another arrangemefnt of elements 2 I, 22 and 23 which may be used in an embodiment of the invention is illustrated. in Fig. 5. Elements which correspond to those fof Fig. l have identical reference numerals, the angles being designated as illustrated in the figure. In the arrangement of Fig. 5 the coupling between inductors 2| and 22 is zero in the absence of disc 23 and, in the presence of disc 23, there exist a plurality of disc positions, dependent upon the angles 0'1 and 0'3, at which the coupling of one of the inductors to the disc 23 is zero. In general, the arrangement of Fig. 5 provides greater coupling of one polarity than of the other polarity.

While in the arrangements of the invention described above, the inductors 2| and 22 are stationary and the disc 23 is rotated about an axis, it will be understood that, in certain modifications of the invention, the disc 23 can be maintained stationary and inductors 2| and 22 can be simultaneously moved relative thereto. In either event, it will be understood that the arrangement .may be considered to comprise and is the full equivalent of a movable inductive coupling means so disposed with reference to one of the inductors that, in a given position of its path of motion. it is substantially uncoupled with at least one of the inductors and, in another given position in its path of motion, it is substantially coupled with both of the inductors.

While there have been described'what are at present considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention,

What is claimed is:

1. An adjustable coupling system comprising, a first inductor, an input circuit connected to said first inductor, a second inductor so disposed in the magnetic field of said first inductor that said second inductor is substantially inductively uncoupled with said first inductor, an output circuit connected to said second inductor, a movable conductive inductive-coupling means substantially nonselective over the frequency range of said system so disposed with reference tosaid inductors that in a given position in its path of motion it is substantially uncoupled with at least one of said inductors and in another position in its path of motion it is substantially coupled with both of said inductors, and means for movirig said coupling means in said path to adjust the coupling'between said inductors.

2. An adjustable coupling system comprising, a first inductor, an input circuit connected to said first inductor, a second inductor so disposed in the magnetic field of said first inductor that said second inductor is substantially inductively uncoupled with said first inductor, an output circuit connected to said second inductor, a movable conductive inductive-couplingmeans substantially nonselective over the frequency range of said system so disposed with reference to said inductors that in a given position in its path of motion it is substantially uncoupled with at least one of said inductors and in other positions in its path of motion on opposite sides of said given position it substantially couples said inductors with a polarity dependent upon the direction in said path from said given position, and means for moving said coupling means in said path and through" said given position to adjust to either inductors.

3. An adjustable coupling system comprising, a first inductor, an input circuit connected to said first inductor, a second inductor so disposed in the magnetic field "of said first inductor that said second inductor is substantially inductively uncoupled with said first inductor, an output circuit connected to said second inductor, a rotatably movable conductive inductive-coupling means substantially nonselective over the fre-' quency range of said system so disposed with reference to said inductors that in a, given position in its path of motion it is substantially uncoupled with at least one of said inductors and in another position in its path of motion it is substantially coupled said path to adjust the coupling between said inductors.

polarity the coupling between said with both of said inductors. Q and means for moving said coupling means in;

is substantially inductively cuit connected to said second inductor, a movable inductive-coupling means substantially nonselective over the frequency range of said system comprising a disc of conductive material so disposed with reference to said inductors that in a given position in its path of motion it is substantially uncoupled with at least one of said inductorsand in another position in itspath of motion it is substantially coupled with both of said inductors, and means for moving said coupling means in said path to adjust the coupling between said inductors.

5. An adjustable coupling system comprising, a first inductor, an input circuit connected to said first inductor, a second inductor so disposed in the magnetic field of said first inductor that said second inductor is substantially inductively'uncoupled with said first inductor, an output circuit connected to said second inductor, a movable conductive inductive-coupling means substantially nonselective over the frequency range of said system so disposed with reference to said inductors that in a given position in its path of motion it is substantially uncoupled with one of said inductors and substantially coupled to the other of said inductors and in another position in its path of motion it is substantially coupled with both of said inductors, and means for moving said coupling means in said path to adjust the coupling between said inductors.

6. An adjustable coupling system comprising, a first inductor, an input circuit connected to said first inductor, a second inductor so disposed in the magnetic field of said first inductor that said second inductor is substantially inductively uncoupled with'said first inductor, an output circuit connected to said second inductor, a movable conductive inductive-coupling means substantially nonselective over the frequency range of said system so disposed with reference to said inductors that in a first given position in its path of motion it is substantially uncoupled with oneof said inductors and substantially coupled withthe other of said inductors, in a second given position I in its path of motion it is substantially uncoupled with said other of said inductors and substantially coupled with said one of said inductors, and in other positions in its path of motion including positions between said given positions it is substantially coupled with both of said inductors, and means for moving said coupling means in said path to adjust the coupling between said inductors.

'7. An adjustable coupling system comprising, a first inductor, a second inductor so disposed in the magnetic field of said first inductor that said second inductor is substantially inductively uncoupled with said first inductor, an output circuit connected to said second inductor, a movable conductive inductive-coupling means substantially nonselective over the frequency range of said system so disposed with reference to said inductors that in a first given position in its path of motion it is substantially uncoupled with one of said inductors and substantially coupled with the other of said inductors, in a second given position in its path of motion it is substantiallyuncoupled with said other of said inductors and substantially coupled with said one of said inductors, and in otherpositions in its path of motion on opposite sides of one of said given positions it substantially couples said inductors with a polarity dependent uponthe direction in said path from said one of said given positions, and means for moving said coupling means in said path through said one of said given positions to adjust to either polarity the coupling between said inductors.

-8. An adjustable coupling system comprising, a first inductor, an input circuit coupled to said first inductor, a second inductor disposed in the magnetic field of said first inductor with the axis of said first inductor normal to the axis of said second inductor whereby said second inductor is substantially inductively uncoupled with said first inductor, an output circuit connected to said second inductor, a movable conductive inductivecoupling means substantially nonselective over the frequency range of said system so disposed with reference to said inductors that in a given position in its path of motion it is substantially uncoupled with at least one of said inductors and in another position in its path of motion it is substantially coupled with both of said inductors, and means for moving said coupling means in said path to adjust the coupling between said inductors.

9. An adjustable coupling system comprising, a first inductor, an input circuit coupled to said first inductor, a second inductor disposed in the magnetic field of said first inductor with the axis of said first inductor normal to the axis of said second inductor whereby said second inductor is substantially inductively uncoupled with said first inductor, an output circuit connected to said second inductor, a conductive inductive-coupling means substantially nonselective over the frequency range of said system, said means being rotatable about an axis normal to the plane including the axes of said inductors and so disposed with reference to said inductors that in a given position in its path of motion it is substantially uncoupled with at least one of said inductors and in another position in its path of motion it is substantially coupled with both of said inductors, and means for moving said coupling means in said path to adjust the coupling between said inductors.

10. An inductive-coupling system comprising, a

. to said second inductor, a movable conductive inductive-coupling means substantially nonselective over the frequency range of said system, said means being rotatable about an axis normal to said plane and intersectingsaid line of centers jand so disposed that in a given position in its path of motion it is substantially uncoupled with at least one of said inductors and in another position in its path of motion it is substantially coupled with both of said inductors, and means for moving said coupling means in said path to adjust the coupling between said inductors.

11. An adjustable coupling system comprising, a first inductor, an input circuit coupled to said first inductor, a second inductor so disposed in the magnetic field of said first inductor that said second inductor is substantially inductively uncoupled with said first inductor, an output circuit connected to said second inductor, a movable conductive inductive-coupling means substantially nonselective over the frequency range of said system so disposed with reference to said inductors that in a given position in its path of motion it is substantially uncoupled with at least one of said inductors and in another position in its path of motion it is substantially coupled with both of said inductors, said inductors and said inductive-coupling means having axes two of which are normal to each other and in a common plane and the other of which is normal to said plane, and means for moving said coupling meansin said path to adjust the coupling between said inductors.

12. An adjustable coupling system comprising, a first inductor, an input circuit connected to said first inductor, a second inductor so disposed in the magnetic field of said first inductor-that the axes of said inductors are in mutually normal 15 g planes and said second inductor is substantially .erence to said inductors that its axis is in the line of centers of said inductors and that in a given position in its path, of motion it is substantially uncoupled with at least one of said inductors and in another position in its path of motion it is substantially coupled with both of said inductors, and means for moving said coupling means in said path'to adjust the coupling between said inductors.

LESLIE F. CURTIS. 

